This invention relates to the testing of hermetically sealed packages to determine whether or not such packages have defects, such as air leaks and the like. More specifically, it pertains to an improved method and system for detecting leaks in such packages without affecting the physical integrity of the package incident to the testing procedure.
Various types of products are packaged in such a manner as to prevent the exchange of air from within the package with the air surrounding the package. Hence, such products as, bacon, wieners, luncheon meats and the like are vacuum packaged in flexible plastic packages. It is contemplated that a hermetically sealed package is sealed incident to a sealing procedure such that the package is sealed tightly enough to preclude the entrance into the package of ambient air and impurities. It is well-known that the free exchange of air through the packaging would allow contaminants to invade the product from without, or it would allow for the loss of product moisture, or in some cases the gain of outside moisture to the product. In each of such instances, the product quality or even product safety would be compromised. It is well-known that a product contained in a hermitically sealed package is known to retain its desired qualities for a longer period of time than if contained within a package which allows free exchange of air through its package boundaries. As indicated, the goal of hermetically sealing a package is to also prevent the intake of impurities from the ambient air which impurities could include bacteria which would have a deleterious effect on the food product packaged within.
Most products today are packaged in a production line at a fairly fast rate. The sealing portion of the packaging line must reliably secure each package within an airtight envelope. However, if there is a malfunction in the sealing equipment, there may be a large number of defective packages produced The defective packages could represent a considerable economic loss to the company producing the product. A more serious problem occurs if defectively sealed products escape quality control checks, and a portion of the defective package products are boxed and shipped to customers. In such an event, the possible deleterious effects to the public are greatly enhanced.
Normally, in the past, defective packages were detected by visual inspection. However, only the larger and more obvious defects can be detected visually by quality control personnel. As production lines speeds have increased, visual inspection becomes a less effective method of detecting leaking packages.
Another method which randomly tests packages removed from a production line is illustrated in U.S. Pat. No. 3,117,441, entitled "Method and Apparatus for Determining Vacuum Conditions in Packaging." The obvious shortcoming of the device illustrated in U.S. Pat. No. 3,117,441, is that it only tests a random sampling of packages and cannot test each package as it passes through a conveyor system. Furthermore, the system as disclosed therein relies upon the concept of reducing the pressure within the test chamber to cause a distension of the package, and then slowly increasing the pressure back to reduce the distension of the package and measuring the rate of retraction of the package to a preselected retracted arrangement. It has been found that this system is subject to great error and will not always accurately detect leaking packages.
Another device used for detecting leaks is illustrated in U.S. Pat. No. 4,024,956, entitled "Method and Apparatus for Detecting Leaks." The method and apparatus as disclosed in this patent is useful in continuously testing for leaks in a series of fluid-type flexible packages which are conveyed along a conveyor path. This apparatus is more specifically designed, however, to be used with packages such as those containing potato chips and the like which have a certain amount of gas sealed within the container. The packages are compressed and the extent of their expansion when they are compressed is measured. Packages which have leaks will not expand in the direction required to measure a "good" package as opposed to one having a defective seal. However, this apparatus and method is not acceptable for use with rigid or semi-rigid packages such as those for cigarettes or bottles of pills where the degree of expansion of the package would be insufficient to make a determination of seal tight integrity.
Another device for determining the integrity of vacuum package is disclosed in U.S. Pat. No. 3,998,091, entitled "Test Apparatus for Determination Quality of Packaging for Vacuum Packaged Products." This device applies a stress on the package to determine the quality of the package by measuring the package deflection resulting from the stress. The device is not acceptable for use on a continuous conveyor line but can only be utilized for the random sampling of packages. Thus it has the obvious shortcoming of not being able to guarantee the quality of each and every package as it passes through the packaging conveyor system. Furthermore, as was indicated as a difficulty associated with the prior device mentioned above, the apparatus and method as disclosed in this patent similarly does not appear to function well for rigid or semi-rigid packages.
Another prior art approach operates on a traced gas principal, wherein sealed and enclosed packages are compressed or otherwise pressurized so that if leakage exists, it is ascertained through the monitoring of the leaking, traced gas. An obvious shortcoming to this method is that in order to properly test a package, a tracer gas must be introduced into the package in some manner. The only other method of conducting a test in this manner is to seal a randomly selected package with a radioactive or other tracer gas included therein, and to then determine whether or not the tracer gas or radioactive gas is detected in an enclosed chamber. This method has the drawback of requiring that random packages be preselected for testing by inserting a tagged or tracer gas therein during the packaging or sealing procedure, which will only be detected with respect to that package if it is a leaker. Such a testing method will basically only determine whether or not the sealing equipment is working properly, but will certainly not test a hermetically sealed package under normal circumstances.
A recent approach to detecting a leak in a package is illustrated in U.S. Pat. No. 4,858,463, entitled "Process and Apparatus for Detecting Leaks in Sealed Packages." The process and apparatus disclosed in this patent is based on the fact that the air leaking from a package into the sealed test chamber in which it is placed will increase the density of the air in the test chamber and as a result the pressure in the test chamber will increase. This increased test chamber pressure then would indicate a leaking package. However, a small change in the temperature of the air in the test chamber (a package temperature greater than the temperature of the air in the test chamber would result in an increasing chamber air temperature during tests) would also increase the air pressure thus erroneously indicating a leaking package. This sensitivity to temperature would greatly impair this device from accurately determining seal integrity of packages in actual practice.
Other apparatus and approaches have been used in detecting leaks and packages which are directed to arrangements which determine whether or not vacuum conditions in such packages have been lost. These techniques likewise, as with previously mentioned apparatus, are basically unsuitable for an accurate testing of a typical hermetically sealed package as it is constructed, filled, and sealed along a typical conveyor system. Furthermore, any testing procedure which will destroy the physical integrity of the package in order to conduct a test for leakage is not deemed to be a proper method of testing with respect to packages which are to be sealed in a normal course of events and which should be tested on a quality control basis. Accordingly, these types of apparatus and prior art methods fail to provide suitable arrangements which enable a rapid and continuous detecting of packages as they are continuously and successably advanced along a typical conveyor system.